The present invention generally relates to electrochemical cells, i.e., batteries, and, more particularly, to a battery having a pressure relief mechanism formed in the container for venting when exposed to excessive pressure.
Conventional alkaline electrochemical cells generally include a steel cylindrical can having a positive electrode, referred to as the cathode, which comprises manganese dioxide as the active material. The electrochemical cell also includes a negative electrode, referred to as the anode, which comprises zinc powder as the active material. In bobbin-type cell constructions, the cathode is typically formed against the interior surface of the steel can, while the anode is generally centrally disposed in the can. Alternately, in jelly-roll cells, the anode and cathode are spirally wound. A separator is located between the anode and the cathode, and an alkaline electrolyte solution simultaneously contacts the anode, the cathode, and the separator. A conductive current collector is commonly inserted into the anode active material, and a collector and seal assembly, which includes a seal member, an inner metal cover, a current collector, and an outer cover, provides closure to the open end of the steel can to seal the active electrochemical materials in the sealed volume of the can.
Cylindrical alkaline electrochemical cells are commonly sealed closed by placing an annular nylon seal in the open end of the steel can and crimping the upper end of the can radially inwardly and over the outer periphery of the seal to compress the seal against the can. However, electrochemical cells commonly employ electrochemically active materials, such as zinc, which generate hydrogen gas during storage and sometimes during or following service use. When the battery can is sealed closed, excessive build-up of high pressure gases within the sealed can may cause damage to the cell and/or the device in which the cell is employed.
One approach to avoiding a potentially excessive build-up of pressure in a cell has been to employ a resealable valve system that periodically releases excessive gas pressure from within the active cell volume. However, the continued periodic release of gas pressure may, in some situations, permit the release of electrolyte solution containing salts and other particulate matter, which may foul the resealable valve. In addition, resealable valve systems generally require additional costly components that are typically quite voluminous.
Other more widely acceptable approaches to venting excessive pressure have included the use of a vent formed in the annular nylon seal, which is intended to rupture upon experiencing an excessive pressure build-up within the cell. For example, U.S. Pat. No. 5,667,912 discloses a current collector assembly having a low profile seal with a thinned portion which is intended to shear when the internal pressure exceeds a predetermined pressure. The conventional ventable seals typically employ a circular thinned region formed in the annular nylon seal. However, the amount of space occupied by the annular seal and the corresponding current collector, inner metal cover, and outer cover, can be significant. The greater the space occupied by the seal and collector assembly, the less space that there is available within the cell for the electrochemically active materials. Consequently, a reduction in the amount of electrochemically active materials provided within the cell generally results in a shorter service life for the cell. It is therefore desirable to maximize the internal volume within an electrochemical cell that is available for the electrochemically active components.
The present invention improves the protective safeguards of an electrochemical cell with an enhanced pressure relief mechanism that allows for the use of a low profile seal assembly for sealing the open end of the cell container. To achieve this and other advantages, and in accordance with the purpose of the invention as embodied and described herein, the present invention provides for an electrochemical cell having conventional components of a container with a closed bottom end, an open top end and side walls extending between the top and bottom ends, and positive and negative electrodes disposed in the container, but also the container having a stress concentrator formed therein for providing pressure relief to vent high pressure gases. The stress concentrator includes first and second stress concentration grooves arranged to cross each other, and a third stress concentration groove having an arcuate configuration and arranged in relation to the first and second stress concentration grooves to define a vent section. The stress concentrator advantageously provides for multiple stress concentration points which offer increased reliability of venting, reduced space required for the vent opening, and which results in significant reduction of bulging in the closed bottom end of the container.
These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings.